Dissolution of synthetic brannerite in acidic and alkaline fluids

Abstract

The dissolution of synthetic brannerite in aqueous media at 40 and 90 °C under atmospheric redox conditions has been studied. At 40 °C, the presence of phthalate as a buffer component in the pH range of 2–6 has little effect on uranium release from brannerite. Bicarbonate increases uranium release and enhances the dissolution of brannerite. Compared to UO 2, brannerite is more resistant to dissolution in bicarbonate solutions. In under-saturated conditions at 90 °C, the dissolution of brannerite is incongruent (preferential release of uranium) at pH 2 and nearly congruent at pH 11. TEM examinations reveal a polymorph of TiO 2 (pH 2 specimen) and a fibrous Ti-rich material (pH 11 specimen) as secondary phases. XPS analyses indicate the existence of U(V) and U(VI) species on the surfaces of specimens both before and after leaching, and U(VI) was the dominant component on the specimen leached in the pH 11 solution.